Gas Sensor Principle & Application

Gas sensor principle
Gas sensors are sensors that measure gas concentration and composition and play an important role in environmental protection and safety monitoring. The gas sensor is used in gases exposed to various components. Due to the large changes in temperature and humidity at the inspection site, there are a large amount of dust and oil mist, etc., so the working conditions are harsh, and the material of the gas to the sensing element Chemical reactions are generated that attach to the surface of the component and tend to degrade their performance. Therefore, the gas sensor has the following requirements: it can detect the allowable concentration of the alarm gas and other standard values ​​of the gas concentration, can work stably for a long time, has good repeatability, fast response, and has little influence on the coexisting substances.

The wave speed and frequency of the surface of the acoustic wave device will drift as the external environment changes. The gas sensor uses this property to coat a surface of the piezoelectric crystal with a gas sensitive film that selectively adsorbs a gas. When the gas sensor interacts with the gas to be tested (chemical or biological, or physical adsorption) When the film quality and conductivity of the gas sensing film are changed, the surface acoustic wave frequency of the piezoelectric crystal is shifted; the gas concentration is different, and the film quality and the conductivity change degree are different, that is, the surface acoustic wave frequency is caused. The changes are also different. An accurate change in the concentration of the reaction gas can be obtained by measuring the change in the frequency of the surface acoustic wave.

Gas sensor principle application

Main parameters and characteristics of gas sensor
Sensitivity: sensitivity to gases

Response time: response speed to the measured gas concentration

Selectivity: refers to the ability of a <a href="https://www.censtry.com">gas sensor</a> to distinguish the gas species under the condition of coexistence of multiple gases: when the measured gas concentration is constant, if other conditions change, the gas sensor output characteristics remain within a specified time. Constant ability temperature characteristics: characteristics of gas sensor sensitivity as a function of temperature. Humidity characteristics: characteristics of gas sensor sensitivity as a function of environmental humidity. Power supply voltage characteristics: characteristics of gas sensor sensitivity as a function of supply voltage Timeliness and interchangeability: The time to reflect the stability of the gas-sensitive characteristics of the component is the timeliness; the consistency of the gas-sensitive characteristics between the components of the same model reflects its interchangeability.

Gas sensor principle application

Gas sensor application
The application of gas sensor mainly includes: detection of carbon monoxide gas, detection of gas gas, detection of gas, detection of Freon 、 11, R12 、, detection of ethanol in exhalation, detection of bad breath in human body, and the like. It converts the gas type and its concentration-related information into electrical signals. According to the strength of these electrical signals, information about the presence of the gas to be tested in the environment can be obtained, so that it can be detected, monitored, alarmed, and passed through the interface. The circuit and computer form an automatic detection, control and alarm system. Due to the wide variety of gases and the different properties, it is impossible to detect all types of gases with one type of sensor. Therefore, many types of sensors that can realize gas-electric conversion can be classified into semiconductor and non-semiconductor according to the materials constituting the gas sensor. At present, the most practical use is the semiconductor gas sensor. Therefore, this paper mainly describes the related principles and applications of semiconductor gas sensors.

The semiconductor gas sensor detects the gas by utilizing changes in physical properties such as electrical conductivity when the gas to be tested is in contact with the surface of the semiconductor. According to the semiconductor and gas interaction changes are limited to the surface of the semiconductor or deep into the semiconductor, can be divided into surface control type and body control type, the former semiconductor surface adsorption of electrons between the semiconductor and the semiconductor, resulting in the conductivity of the semiconductor When the physical properties change, but the internal chemical composition does not change, the latter semiconductor reacts with the gas to change the internal composition of the semiconductor and change the conductivity. According to the physical characteristics of semiconductor changes, it can be divided into resistive and non-resistive types. When a sensitive semiconductor material is used to contact a gas, its resistance value changes to detect the composition or concentration of the gas. It is based on the adsorption and reaction of the gas, so that some of its relationship characteristics are changed without direct or indirect detection of the gas, such as diode volt-ampere characteristics and threshold voltage changes of the field effect transistor to detect the gas to be measured.